Recent magneto-optical discs have increasingly large capacities, and accordingly can allow an increasing number of defective sectors to be therein. This means increase in the volume of information contained in DMA (Defect Management Area) which is an address list of defective sectors in the magneto-optical disc. A result is a tendency of prolonged time for loading (a set of procedures which immediately follow disc insertion). For example, a magneto-optical disc having a capacity of 1.3 GB needs a loading time of about twelve seconds. The capacity of magneto-optical disc will be increased further in the future, which could lead to a longer loading time. So, there is a need for a technique to quicken the loading or reducing the loading time.
FIG. 8 shows a conventional disc drive A10. When a magneto-optical disc B10 is loaded, a CPU 110 reads a control track B11 of the magneto-optical disc B10 and identifies a type of the disc.
Once the type is identified, the CPU 110 obtains physical addresses on the magneto-optical disc B10, of areas where DMA information B12 is stored. Then, the CPU 110 reads a total of four areas, starting from two areas in an innermost region and then two other areas in an outermost region of a recording area B13 of the magneto-optical disc B10, thereby obtaining and then storing the DMA information B12 in a DMA information storage area 120D of a RAM 120 serving as a buffer memory.
The DMA information B12 includes PDL (Primary Defect List) and SDL (Secondary Defect List). These are addresses lists of defective sectors on the magneto-optical disc B10.
Description will be made specifically for the PDL. Now, compare FIG. 9 and FIG. 10: when a defective sector is detected in a zone during the physical formatting of a magneto-optical disc B10, the defective sector is skipped by the step of writing initializing data, and this zone which includes the defective sector is extended into a spare zone in order to provide a predetermined number of flawless sectors by using a spare sector available in the spare zone. The physical address- of the defective sector is recorded in the DMA information B12 for management of the medium. Such a defect, i.e. a defect in which an address can be assigned while skipping defective sectors, is called primary defect. A collection of addresses of the defective sectors that fall into the category of primary defect is called PDL.
Now about the PDL. Compare FIG. 9 and FIG. 11: when a defective sector is detected in a zone while writing data, the data is written onto another sector in the spare zone, in place of the defective sector. Then, the address of the defective sector and the address of the spare sector which replaced the defective sector are recorded onto the DMA information B12. Such a defect, i.e. a defect in which a replacing spare sector can be specified by address conversion, is called secondary defect. A collection of addresses of the defective sectors that fall into the category of secondary defect is called SDL.
When loading a magneto-optical disc B10, logical addresses given by the host C10 must be converted to physical addresses. For this reason, it is always necessary to read DMA information B12, and in order to verify integrity of the DMA information B12, all the four pieces of DMA information B12 must be read. This is to overcome a possible accidental situation in which power supply is cut off during sector conversion operation for a newly found second defect detected while data is written onto the magneto-optical disc B10. In such an accidental situation, the DMA information B12 is potentially not updated completely due to interruption by an abnormal shutdown, and then, each piece of the DMA information B12 will not agree with each other. In order to overcome such a situation, it is necessary to use the most reliable DMA information B12.
When the loading is completed along the above procedure, the CPU 110 of the disc drive A10 can begin data reading and/or writing with the magneto-optical disc B10, in response to access commands from the host C10 and with reference to the PDL and SDL found in the obtained DMA information B12.
Particularly, when reading data from the recording area B13 of the magneto-optical disc B10, data transfer is performed via a cache area 120C of the RAM 120. Data copied onto the cache area 120C is held until the cache area 120C is over flown. Thus, when the host C10 requests reading of data from the same address as before, the CPU 110 does not need to go back to a seek operation control which involves mechanical movement of the reading heads, but simply can pick and transfer the copied data in the cache area 120C directly to the host C10.
Then, when an EJECT key is operated or an EJECT command is sent from the host C10 for ejecting the magneto-optical disc B10 from the disc drive A10, an unloading (a set of procedures for final ejection) operation is performed, which includes invalidation of the data remaining in the cache area 120C.
Now, when the same magneto-optical disc B10 as the previous disc is inserted again into the disc drive A10, conventionally, the CPU 110 simply and always performs the operation of reading all the four pieces of DMA information B12 from the magneto-optical disc B10 whether or not the DMA information B12 is the same.
Likewise, any data remaining in the cache area 120C after an unloading is invalidated. Thus, when the same magneto-optical disc B10 as the previous disc is inserted again into the disc drive A10 for loading, the CPU 110 begins the whole process of reading data newly from the magneto-optical disc B10 through the seek control operation, and then transfers the read data via the cache area 120C to the host C10.
In practical use of the drive, the user often does such a practice, i.e. that he ejects a magneto-optical disc B10 out of the disc drive A10 and then inserts the same magneto-optical disc B10 again into the disc drive A10, causing the drive to repeat the loading process.
For example, the user of ten wants to eject a magneto-optical disc B10 from the disc drive A10, in an attempt to check what is written on the label pasted onto the label region of the magneto-optical disc B10, to paste a label onto the label region, or to write a memo onto the label.
Another example is right after storing important data in a magneto-optical disc B10. The user often wants to protect the data from accidental erasure, and thus wants to turn on a write-protect switch or a tab on the hard case of the magneto-optical disc B10 which prevents further writing onto the disc.
However, even if the same magneto-optical disc B10 as the ejected is inserted again, and the host C10 sends a data access command to the disc drive A10 during the second loading, the CPU 110 is unable to begin the conversion process of the specified logical addresses to the physical addresses since the DMA information B12 containing the PDL and SDL is not available until the loading is complete. Thus, the CPU 110 must withstand the commanded accessing operation until the loading is over, resulting in a problem of delayed response to the host C10. The time necessary for this response becomes longer as the capacity of the magneto-optical disc B10 increases.
At the time of the second loading, the cache area 120 of the RAM 120 already holds some data copied from the magneto-optical disc B10, and there is a high probability that this data is hit. Yet, in the second loading, all the data remaining in the cache area 120C has been invalidated by the unloading process performed right before. Thus, when the second loading is complete and the host C10 sends a command for data reading, the CPU 110 cannot try to hit the data in the cache area 120C, and then always has to perform the seek operation which involves mechanical movement of the reading heads. Accordingly, a longer time must be spent before the host C10 is notified of the completion of the commanded task of data reading. So, again, there is a problem of delayed response to the host C10.